Large fiberglass boats and other fiberglass structures have been and are being made by following the hand layup procedures used in placing layers of fiberglass cloth, bonded with resin over a mold. While such hand layup structures have been and are satisfactory for many products, there are potentially other products such as liquid natural gas tanks, wherein a more efficient use of fiberglass requires uniform tensioning of the fibers, and their orientation in the direction of the stresses. Moreover, the use of continuous fibers in a machine wound structure greatly reduces the dependence upon the resin to transfer loads through shear. In addition overlaps of fiberglass, as are required when small pieces of fiberglass material are used, are eliminated, when a machine wound structure is being manufactured. The machine windings over a mold result in structures that are of higher quality, lighter, and amenable to accurate stress analysis.
For these reasons smaller high pressure tanks and rocket cases have been previously wound from fibers. These smaller tanks have been and are being made in one piece, using a male mold that is extracted through a filler hole. These smaller winding machines usually have a fixed base for the fiberglass supply system, and the mold rotates about two axes to generate a desired winding pattern to form the fiberglass tank. In regard to these smaller high pressure tanks, the stresses due to internal pressure, are so high relative to those imposed by the weight of the tank, that the tank is mounted on a saddle without using any mounting fittings previously built into a tank.
Conversely, very large tanks, over 100 inches in diameter, which operate at low pressures, with the principal load being due to the mass of the contents, have relatively thin tank walls in comparison to their diameter, and act mostly like a membrane. A horizontal equator mounting of these large LNG spherical tanks is undertaken. Moreover these LNG tanks result from using a new type of winding machine, which builds large hemispherical halves of the LNG tanks, using a mold which pivots about one axis, rather than about two axes, as often occurs when small tanks are being manufactured.